What controls end of injection?

[Trailnewt]

I'm trying to educate myself on the control systems in my AHU engine. I think this info also applies to ALH, AFN, 1Z.
By searching the threads on this forum I have learned that the ECU controls the timing of start of injection based on a number of parameters including fuel temp., water temp., barometric pressure, etc. I also understand that the ECU can only control injection timing within a limited range dependent on the position of the injector pump. I also understand (or think I understand) that the stiffness of the springs in the nozzles will have some effect on injection timing since it will take the pump a tiny bit more time to overcome a stiff spring than a soft one.
What I don't understand is what controls the end of injection? Is this purely a function of the duration of fuel pressure from the pump and the stiffness of the springs in the injectors or is it more complicated than that? Is there some control that the ECU has over this?
Another question that interests me is what are all the various factors that the ECU takes into account when adjusting timing? I listed some of them above but have a feeling there must be more. Can a knowledgeable chip tuner adjust for all of these variables?
Thanks in advance for your contributions to my further education.

 

[jsrmonster]

I'm trying to educate myself on the control systems in my AHU engine. I think this info also applies to ALH, AFN, 1Z.
By searching the threads on this forum I have learned that the ECU controls the timing of start of injection based on a number of parameters including fuel temp., water temp., barometric pressure, etc. I also understand that the ECU can only control injection timing within a limited range dependent on the position of the injector pump. I also understand (or think I understand) that the stiffness of the springs in the nozzles will have some effect on injection timing since it will take the pump a tiny bit more time to overcome a stiff spring than a soft one.
What I don't understand is what controls the end of injection? Is this purely a function of the duration of fuel pressure from the pump and the stiffness of the springs in the injectors or is it more complicated than that? Is there some control that the ECU has over this?
Another question that interests me is what are all the various factors that the ECU takes into account when adjusting timing? I listed some of them above but have a feeling there must be more. Can a knowledgeable chip tuner adjust for all of these variables?
Thanks in advance for your contributions to my further education.

The piston walks back down the camplate in the pump, and the main spring in the injector overcomes force of fuel pressure on the pintle area inside the nozzle, and closes injector, and delivery valve (in pump head) prevents combustion pressures from forcing fuel back thur system. A column of fuel is ready for next injection event like a bullet in the chamber.
Jeff

 

[Trailnewt]

Ah.

So the ECU can control start of injection (within limits) but the nature of the pump mechanism controls end of injection.

Thank you!

 

[hendomatic]

Would it not be the position of the quantity adjuster control collar that controls the end of injection?
Injection Pump Thread

 

[jsrmonster]

Would it not be the position of the quantity adjuster control collar that controls the end of injection?
Injection Pump Thread

Actually the slide collar determines amount of charge loaded in the breech, while the camplate aims it early or late!
There is some good reading about this if you search!

 

[hendomatic]

Actually the slide collar determines amount of charge loaded in the breech, while the camplate aims it early or late!
There is some good reading about this if you search!

That would seem to be at odds with documentation that I referenced.

Injection Pump Thread

 

[Trailnewt]

So if the collar controls the end of injection and, according to the linked thread, the collar is controlled by the ECU, then the ECU controls both start of injection and end of injection (within the physical limitations of the static timing and the pump internals).
Since the ECU doesn't "know" that we have replaced the stock nozzles with a different size or type part of what a chip tuner can do for us is to change the timing of both injection start and injection end for the performance characteristics we want from the non-stock nozzles, right?
Brent

 

[Conan]

Do all TDIs deliver fuel twice per cycle?

 

[jsrmonster]

Do all TDIs deliver fuel twice per cycle?

No, you can rotate your fuel lines up, remove and install injectors (outside cylinders) and watch them fire in the wind once per each TDC event (as you energize the starter).
Jeff

 

[TopherDI]

wait for it.............................

 

[oil_me]

Perhaps he's referring to: #1 pilot injection and #2 main injection?

Do all TDIs deliver fuel twice per cycle?

 

[Drivbiwire]

Yes, the TDI has two distinct injection events. These are controlled by the injector with the supplied pressure from the pump. The Injector breaks up the single pressure pulse provided by the pump into the two injection sequences which last approx 5-15 miliseconds. The duration and volume are completely controlled by the positioning of the control collar in the pump. It's not something you can see or watch with the naked eye by turning the lines upward...

The cam plate is what determines the "Rate" of the pressure build up and to a certain extent the peak pressure.

Collar controls EOI and Volume.
Cam Plate controls pressure rate and factors into peak pressure by virtue of the height of each peak for a given profile.
Injector controls Pilot and Primary sequencing
#3 injector provides feedback on SOI at the injector, due to compressibility and variances that occur with temperature and the effects on the speed of the pressure pulse to each injector.

The pump simply provides a single pulse that is broken up at the injector. The same applies to the VE, PD, and CRI systems the difference is how the injectors are controlled.

 

[Trailnewt]

I am curious about the series of small peaks and valleys of pressure shown on the graph at each spring opening. Are these caused by the spring oscillating between a fully open state and a less-than-fully-open state as pressure builds and releases from the holes in nozzle? Does this series of oscillations contribute to fuel atomization?
I have seen it said that fuel atomization is greater at higher pressures but have had a hard time figuring out why this is the case. I would think that nozzles are manufactured to provide optimum atomization at a certain range of pressures and that atomization would decrease both below and above these pressures. Does this series of oscillations speed up in higher pressure injectors (stiffer springs) and thereby create better atomization at higher pressures for any given nozzle?
Brent

 

[Drivbiwire]

Those peaks are called "noise" caused by the momentary drop in pressure as the injector opens. You get fluctuations during this .3-4.0 millisecond time frame caused by the sudden drop and increase in pressure being supplied to the nozzle.